The DF3/MUC1 gene encodes a high molecular weight membrane-associated glycoprotein with a mucin-like external domain. The MUC1 glycoprotein is expressed on the apical borders of secretory epithelial cells and aberrantly at high levels over the entire surface of breast, prostate, lung and other types of carcinoma cells [Kufe et al.(1984) Hybridoma 3:223-232; Perey et al. (1992) Cancer Res. 52:2563-2568]. Estimates indicate that over 500,000 new tumors overexpressing MUC1 are diagnosed each year.